Metabolic changes which occur in cultures of Pseudomonas aeruginosa prior to, and during, pyocyanine production, as well as the biochemical precursors of the pigment, were investigated. Production of the pigment was found to occur at the end of the logarithmic growth phase and was paralleled by cell death and autolysis. The degradation products of L-tryptophan, namely 3-hydroxyanthranilate and.